1. Field of the Invention
The present invention relates to a steering apparatus for a four-wheeled vehicle. This steering apparatus is used to transmit a steering force applied to a handle, which is connected to a steering shaft, through a reduction gear mechanism, a steering lever and a pair of tie rods to knuckles, which support right and left wheels, respectively.
2. Description of the Related Art
A steering apparatus for a four-wheeled vehicle, particularly, a low-speed utility vehicle is provided with a rack-and-pinion reduction gear mechanism (steering gear mechanism). The rack-and-pinion reduction gear mechanism includes a pinion connected to a steering shaft, and a rack engaged with the pinion and capable of moving to right and left, i.e., in the direction along the width of a vehicle. The opposite ends of the rack are connected to right and left knuckles by tie rods, respectively.
The long rack of the rack-and-pinion reduction gear mechanism is disposed so as to extend and move laterally, and hence the right and left tie rods are inevitably short. In case that such short tie rods are used, the position of the rack with respect to the back-and-forth direction cannot be spaced a long distance apart from the position of the joint of the knuckle and the tie rod. Therefore, the flexibility of the positioning of the rack is strictly restricted.
If the rack is disposed far ahead of the joints of the knuckles and the tie rods with respect to the back-and-forth direction to secure a wide space for driver""s feet on a step, the mounting angles of the tie rods become large. As a result, a high steering force is necessary. Thus, the position of the rack along the back-and-forth direction must be in a narrow range to achieve a low steering force by making the mounting angles of the tie rods small. On the other hand, the mounting angles of the tie rods must be large to secure a wide space for driver""s feet. As a result, a high steering force is inevitably caused.
Another type of steering apparatus includes a spur gear type reduction gear mechanism with a set of pinion and spur gear instead of rack and pinion. Long tie rods can be used because the spur gear does not need a wide lateral space. Even if the reduction gear mechanism is disposed far ahead of the joints of the knuckles and the tie rods, the mounting angles of the tie rods can be small. As a result, a low steering force can be achieved. This kind of steering apparatus with the spur gear type reduction gear mechanism is disclosed in Japanese Laid-Open Publication No. 292224/1992.
As shown in FIG. 10, the spur gear type reduction gear mechanism, which is disclosed in Japanese Laid-Open Publication No. 292224/1992, includes an input pinion 139, a spur gear type steering gear 140 with external teeth which are engaged with the pinion 139, and a gear case (steering gear box) 130 which contains the pinion 139 and the steering gear 140. The pinion 139 is disposed in front of the steering gear 140. Therefore, the distance D0 between the axis of a pinion shaft 127 holding the pinion 139, and the axis of a lever shaft 135 holding the steering gear 140 is relatively long, and hence the gear case 130 has a relatively large size along the back-and-forth direction. Furthermore, the gear case 130, which contains the small diameter pinion 139 and the big diameter handle 140, has a complicated shape having a front protrusion 130a. As a result, the gear case 130 requires time-consuming processing. The gear case 130, which has a large size along the back-and-forth direction, restricts the flexibility of the position of the gear case 130 along the back-and-forth direction on a vehicle and entails the following problems.
FIG. 2 illustrates a four-wheeled vehicle to which the present invention is applied as mentioned hereinafter. Suppose that the gear case 130 of the prior steering apparatus shown in FIG. 10 is installed on the vehicle shown in FIG. 2, instead of a gear case 30 which is included in a steering apparatus in accordance with the present invention. If the gear box 130 is disposed in a far forward region to provide a wide foot space S1, the pinion shaft 127, which corresponds to the pinion shaft 27 shown in FIG. 2, is positioned at an excessively forward position and the elevation xcex1 of a steering shaft joined to the pinion shaft 127 is small. Consequently, a universal joint 26 joining the lower end of the steering shaft 15 and the pinion shaft 127 is unable to operate smoothly. If the gear case 130 is shifted backward to increase the elevation xcex1 of the steering shaft 15, the foot space S1 is reduced and operator""s comfortableness is deteriorated.
Accordingly, it is an object of the present invention to provide a steering apparatus with a spur gear type reduction gear mechanism which has a gear case of small, simple construction. The gear case is capable of being installed at a position within a wide range, of providing satisfactory steering feeling and of allowing a wide foot space for the driver.
The present invention is also intended to eliminate backlash in the reduction gear mechanism by a simple mechanism and to give the driver an improved steering feeling.
According to the present invention, a steering apparatus for a four-wheeled vehicle comprises: a steering shaft adapted to be rotated by a handle; a reduction gear mechanism operatively connected to the steering shaft; the reduction gear mechanism including a pinion gear on an input side, a steering gear on an output side, the steering gear having internal teeth which are engaged with the pinion gear, a gear case in which the pinion gear and the steering gear are housed, and a pinion shaft on which the pinion gear is mounted, the pinion shaft being connected to the steering shaft; a steering lever operatively connected to the reduction gear mechanism; right and left tie rods operatively connected to the steering lever; and right and left knuckles operatively connected to the right and the left tie rods, respectively; a lever shaft on which the steering gear is mounted and being combined with the steering lever.
Preferably, the steering gear has a rim extending along an outer periphery of the steering gear, the internal teeth being formed in an inner surface of the rim.
Preferably, the steering gear is formed as a sector shape of which a center corresponds to an axis of the lever shaft, the pinion gear being included completely in a region covered by the steering gear, a curved slot being formed in a wall of the steering gear, the pinion shaft being inserted into the curved slot.
Preferably, the steering apparatus further comprises a spring by which the lever shaft is biased so that the internal teeth is pressed against the pinion gear.
Preferably, the lever shaft has first and second end portions on first and second sides which are located on opposite sides with respect to a position at which the steering gear is connected to the lever shaft, the first end portion being supported by a bearing on the gear case and the second end portion being supported with a radial clearance by a bearing hole formed in the gear case.
Preferably, the clearance between the bearing hole and the lever shaft is formed so as to permit the lever shaft to move only in a direction in which the lever shaft is biased by the spring.
Preferably, the spring is disposed on the second side on which the bearing hole is formed.
Preferably, the spring comprises a compression coil spring and a plunger which is biased rearward by the compression coil spring to press the second end portion of the lever shaft rearward.
Preferably, the plunger includes a recess which is in close contact with a front surface of the lever shaft.
Preferably, the plunger includes a V-shaped groove which is in contact with a front surface of the lever shaft.
Preferably, the plunger includes a flat surface which is in contact with a front surface of the lever shaft.
Preferably, the spring is disposed on the first side on which the bearing is disposed.
Preferably, the spring comprises a compression coil spring and a plunger which is biased rearward by the compression coil spring to press the second end portion of the lever shaft rearward.
Preferably, the plunger includes a recess which is in close contact with a front surface of the lever shaft.
Preferably, the plunger includes a V-shaped groove which is in contact with a front surface of the lever shaft.
Preferably, the plunger includes a flat surface which is in contact with a front surface of the lever shaft.
Preferably, the bearing has a convex inner surface on which the lever shaft is supported so that the lever shaft is able to swing back-and-forth.
Preferably, the gear case is provided in its front end portion with an upper boss and a bottomed lower boss for supporting the pinion shaft, a lower end portion of the pinion shaft being fitted in a bore formed in the lower boss, and an upper end portion of the pinion shaft being supported in a ball bearing which is fitted in the upper boss.